Expandable spinal implant having interlocking geometry for structural support

ABSTRACT

An expandable spinal implant including at least two expandable branch portions extending generally along a longitudinal axis and each including a fixed end portion and an opposite movable end portion with the fixed end portions coupled together adjacent a base portion of the implant. A first of the branch portions includes at least one transverse projection having opposite axially-facing outer surfaces. A second of the branch portions defines at least one transverse recess having opposing axially-facing inner surfaces. The transverse projection is positioned within and displacable along the transverse recess with the outer surfaces of the projection positioned in close proximity with the inner surfaces of the recess to provide structural support to the implant subsequent to expansion. In one embodiment, the branch portions are separated from one another by at least one slot including a narrow portion that defines the close fitting transverse projection and transverse recess.

CROSS REFERENCE TO RELATED APPLICATIONS

The subject application is a continuation of U.S. patent applicationSer. No. 10/897,837 filed Jul. 23, 2004 now U.S. Pat. No. 7,678,148, thecontents of which are hereby incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates generally to the field of expandablespinal implants, and more particularly relates to expandable spinalimplants having interlocking geometry for structural support.

BACKGROUND

There have been numerous attempts to develop a spinal implant to replacea damaged or degenerated natural spinal disc and to maintain sufficientstability of the intervertebral disc space between adjacent vertebrae,at least until arthrodesis is achieved. These types of spinal implantshave taken many forms.

For example, some spinal implants are designed to expand in such amanner as to restore and/or maintain the natural anatomic angle betweenthe adjacent vertebrae. To accomplish this result, some implant designsinclude multiple branches having stationary ends that are attached orotherwise coupled together and movable ends that remain unattached so asto allow the movable ends to expand apart relative to one another toprovide the implant with a select taper angle corresponding to thenatural anatomic angle between the adjacent vertebrae. Expansion of theimplant typically relies on axial displacement of an expansion member orwedge along tapered inner surfaces defined by the branches. One exampleof such an implant design is illustrated and described in U.S. Pat. No.6,436,140 to Liu et al., the contents of which are incorporated hereinby reference.

Expandable spinal implants typically rely on relatively slender orweakened structures or features that allow for material deformation ofcertain portions of the implant, which in turn facilitates expansion ofthe implant in one or more directions. However, the slender or weakenedfeatures that allow for material deformation tend to compromise thestructural integrity of the implant and reduce resistance to loading,particularly resistance to buckling and shear loads exerted onto thespinal implant by the adjacent vertebrae. Accordingly, incorporation offeatures into the spinal implant which facilitate expansion may resultin a reduction in the overall structural integrity of the implant.

Thus, there is a general need in the industry to provide an improvedexpandable spinal implant. The present invention satisfies this need andprovides other benefits and advantages in a novel and unobvious manner.

SUMMARY

The present invention relates generally to an expandable spinal implant.While the actual nature of the invention covered herein can only bedetermined with reference to the claims appended hereto, certain formsof the invention that are characteristic of the preferred embodimentsdisclosed herein are described briefly as follows.

In one form of the present invention, an expandable spinal implant isprovided which includes a body extending generally along a longitudinalaxis between first and second end portions and defining at least oneslot extending from the first end portion toward the second end portionto provide the body with at least two expandable branch portions coupledtogether adjacent the second end portion. The slot includes a narrowportion defining close fitting interlocking features between the branchportions to provide structural support to the implant subsequent toexpansion.

In another form of the present invention, an expandable spinal implantis provided which includes at least two expandable branch portionsextending generally along a longitudinal axis and each including a fixedend portion and an opposite movable end portion with each of the fixedend portions coupled together adjacent a fixed base portion of theimplant. A first of the branch portions includes at least one transverseprojection having opposite axially-facing outer surfaces, and a secondof the branch portions defines at least one transverse recess havingopposing axially-facing inner surfaces. The transverse projection ispositioned within and displacable along the transverse recess with theouter surfaces of the projection positioned in close proximity withrespective ones of the inner surfaces of the recess to providestructural support to the spinal implant subsequent to expansion.

In another form of the present invention, an expandable spinal implantis provided which includes at least two expandable branch portionsextending generally along a longitudinal axis and each including a fixedend portion and an opposite movable end portion with each of the fixedend portions coupled together adjacent a fixed base portion of theimplant. A first of the branch portions includes a first bone engagingsurface adapted to engage an adjacent vertebra and defines at least oneprojection arranged transverse to said first bone engaging surface. Asecond of the branch portions includes a second bone engaging surfaceadapted to engage an adjacent vertebra and defines at least one recessarranged transverse to the second bone engaging surface. The projectionis positioned within and displacable along the recess to providestructural support to the spinal implant subsequent to expansion.

In another form of the present invention, an expandable spinal implantis provided which includes at least two expandable branch portionsextending generally along a longitudinal axis and coupled together toallow relative pivotal movement therebetween about a pivot axis. A firstof the branch portions includes at least one projection having an outersurface extending generally along a radial arc relative to the pivotaxis. A second of the branch portions defines at least one recess havingan inner surface extending generally along the radial arc. Theprojection is positioned within and displacable along the recess withthe outer surface of the projection positioned in close proximity withthe inner surface of the recess to provide structural support to thespinal implant subsequent to expansion.

In another form of the present invention, an expandable spinal implantis provided which includes at least two expandable branch portionsextending generally along a longitudinal axis and each including a fixedend portion and an opposite movable end portion, with each of the fixedend portions coupled together at a fixed base portion of the implant.The fixed base portion of the implant has an outer surface facing awayfrom the branch portions and defining a concave curvature to facilitatetransverse expansion of the implant.

It is one object of the present invention to provide an improvedexpandable spinal implant. Further objects, features, advantages,benefits, and aspects of the present invention will become apparent fromthe drawings and description contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an expandable spinal implant according to oneform of the present invention, as shown in a non-expanded state.

FIG. 2 is an end view of the expandable spinal implant illustrated inFIG. 1.

FIG. 3 is a cross-sectional view of the expandable spinal implantillustrated in FIG. 2, as taken along line 3-3 of FIG. 2.

FIG. 4 is a side view of the expandable spinal implant illustrated inFIG. 1, as shown in an expanded state.

FIG. 5 is a side view of an expandable spinal implant according toanother form of the present invention, as shown in a non-expanded state.

FIG. 6 is a side view of the expandable spinal implant illustrated inFIG. 5, as shown in an expanded state.

FIG. 7 is a side view of an expandable spinal implant according toanother form of the present invention.

FIG. 8 is a side perspective view of an expandable spinal implantaccording to another form of the present invention.

FIG. 9 is a side view of an expandable spinal implant according toanother form of the present invention, as shown in a non-expanded state.

FIG. 10 is a side view of the expandable spinal implant illustrated inFIG. 9, as shown in an expanded state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation on the scope of theinvention is hereby intended, and that alterations and furthermodifications in the illustrated devices, and further applications ofthe principles of the invention as illustrated herein are contemplatedas would normally occur to one skilled in the art to which the inventionrelates.

Referring to FIG. 1, illustrated therein is an expandable spinal implant20 according to one form of the present invention. The spinal implant 20extends along a longitudinal axis L and is configured to expandgenerally along a transverse axis T so as to distract an intervertebraldisc space and/or to restore or maintain lordosis between the adjacentvertebrae. However, it should be understood that expansion of the spinalimplant 20 may occur in multiple directions and along multiple axes. Anexpansion mechanism serves to transition the spinal implant 20 from theinitial configuration illustrated in FIG. 1 toward the expandedconfiguration illustrated in FIG. 4. Further details regarding theexpansion of the spinal implant 20 will be discussed below.

The spinal implant 20 is preferably formed of a biocompatible material.In one embodiment, the spinal implant 20 is formed of a medical gradealloy such as, for example, titanium. However, the use of other metallicmaterials are also contemplated, including stainless steel and stainlesssteel alloys, titanium and titanium alloys, shape-memory alloys, cobaltchrome alloys, or any combination of metallic materials. Additionally,it should be understood that forming the spinal implant 20 from anon-metallic material is also contemplated. For example, in otherembodiments, the spinal implant 20 may be formed of a polymericmaterial, including, for example, a non-resorbable polymer such aspolyetheretherketone (PEEK) or a resorbable polymer such as polylactate(PLA). In further embodiments, the spinal implant 20 may be formed ofbone or bone substitute materials. Examples of other suitable materialsfor forming the spinal implant 20 include composite polymers,non-reinforced polymers, carbon-reinforced polymer composites, carbonfiber, PMMA, calcium hydroxide, ceramics, polylactide, polyglycolide,tyrosine-derived polycarbonate, polyanhydride, polyorthoester,polyphosphazene, calcium phosphate, calcium hydroxide, hydroxyapatite,bioactive glass, or any combination of these materials.

The spinal implant 20 includes a proximal end portion 22 a and a distalend portion 22 b. In one embodiment, the spinal implant 20 is generallycomprised of an upper branch portion 24 and a lower branch portion 26,each extending generally along the longitudinal axis L andinterconnected to one another adjacent the proximal end portion 22 a viaa fixed base portion 28. However, it should be understood that thespinal implant 20 may define any number of branch portions, includingthree, four, or five or more branch portions. As will be discussedbelow, actuation of the expansion mechanism causes the branch portions24, 26 to separate or splay apart to provide the spinal implant 20 witha cross sectional dimension adjacent the distal end portion 22 b that isgreater than the cross sectional dimension adjacent the proximal endportion 22 a.

In the illustrated embodiment, the branch portions 24, 26 are coupled tothe fixed base portion 28 in such a manner as to allow the branchportions 24, 26 to move relative to one another to provide for expansionof the spinal implant 20. In one embodiment, expansion of the spinalimplant 20 results from relative pivotal movement of the branch portions24, 26 about a pivot axis P positioned along the fixed base portion 28adjacent the proximal end portion 22 a. However, other types of relativemovement between the branch portions 24, 26 are also contemplated asfalling within the scope of the present invention. In a furtherembodiment, the fixed base portion 28 is relatively thin or slender andhas a predetermined configuration that provides for controlleddeformation or buckling in a predetermined and repeatable fashion. Inthis manner, expansion of the spinal implant 20 can be correspondinglycontrolled via controlling the positioning of the pivot axis P and therelative orientation and positioning of the upper and lower branchportions 24, 26. In the illustrated embodiment, the fixed base portion28 has a curved or arcuate configuration defining a concave outersurface 29 to facilitate expansion of the spinal implant 20 and toprovide a degree of control over the expansion characteristics of thespinal implant 20. However, other configurations of the fixed baseportion 28 are also contemplated as falling within the scope of thepresent invention.

In one embodiment of the invention, the branch portions 24, 26 areformed integral with the base portion 28 to define a single-piece,unitary spinal implant 20. In this manner, the base portion 28 flexiblyinterconnects the branch portions 24, 26 so as to allow for expansion ofthe spinal implant 20 via flexible material deformation of the branchportions 24, 26 and/or the fixed base portion 28. The interconnectionbetween the fixed base portion 28 and the branch portions 24, 26 acts ina hinge-like manner during expansion of the spinal implant 20 to providefor substantially independent movement of the branch portions 24, 26.Although the illustrated embodiment of the spinal implant 20 utilizesintegrally connected branch portions 24, 26, it is also contemplatedthat the branch portions 24, 26 may be formed separately and connectedtogether to form a multi-piece implant assembly. In another embodiment,the branch portions 24, 26 may be pivotally attached to the base portion28 or directly to one other via a hinge or pivot pin such that thespinal implant 20 may be expanded without relying on flexible materialdeformation. Other suitable means for coupling the branch portions 24,26 together to provide for expansion of the spinal implant 20 are alsocontemplated, including forming or coupling of the branch portions 24,26 directly to one another without the use of a fixed base portion 28.

In the illustrated embodiment of the invention, expansion of the spinalimplant 20 occurs in response to axial displacement of an expansionmember or wedge 30 generally along the longitudinal axis L between thebranch portions 24, 26. Axial displacement of the expansion member 30 inturn causes the branch portions 24, 26 to separate or splay apart,thereby expanding the spinal implant 20 along the transverse axis T.Specifically, as illustrated in FIG. 3, the expansion member 30 isslidably displaced along opposing tapered surfaces 32, 34 defined by thebranch portions 24, 26, which in turn wedges the branch portions 24, 26apart to expand the spinal implant 20 along the transverse axis T.

In a further embodiment, the tapered surfaces 32, 34 define a retentionelement or interlock feature 36 adjacent the distal end portion 22 b ofthe implant 20 which is configured to retain or lock the expansionmember 30 in a select axial position relative to the spinal implant 20and also maintains the spinal implant 20 in a select expandedconfiguration. In the illustrated embodiment, the retention element 36comprises a pair of opposing notches or recesses 38 a, 38 b sized andshaped to receive a corresponding portion of the expansion member 30therein. In one embodiment, the notches 38 a, 38 b have a box-likeconfiguration defining opposing axially-facing surfaces that preventaxial movement of the expansion member 30 relative to the implant 20, aswell as opposing laterally-facing surfaces that prevent lateral movementof the expansion member 30 relative to the implant 20. As a result,positioning of the expansion member 30 within the notches 38 a, 38 balso serves to resist loading exerted onto the spinal implant 20 by theadjacent vertebrae such as, for example, transverse or lateral loadingand compressive loading adjacent the distal end portion 22 b of theimplant 20. Although the retention element 36 has been illustrated anddescribed as comprising a pair of notches 38 a, 38 b, it should beunderstood that other types and configurations of retention elements orinterlock features are also contemplated. For example, the retentionelement 36 may alternatively comprise ratchets, internal threads, orother suitable features configured to engage a corresponding portion ofthe expansion member 30.

Although expansion of the spinal implant 20 has been illustrated anddescribed as occurring in response to axial displacement of theexpansion member 30 along the branch portions 24, 26, it should beunderstood that in other embodiments of the invention, rotational orpivotal displacement of an expansion member 30 relative to the branchportions 24, 26 may be used to cause the spinal implant 20 to expand.Other types of relative displacement between the expansion member 30 andthe branch portions 24, 26 are also contemplated for use in associationwith the present invention, including, for example, displacement of theexpansion member 24 in directions transverse to the longitudinal axis L.In another embodiment, an instrument or tool (not shown) may be providedthat is configured to engage the branch portions 24, 26 and drive thebranch portions 24, 26 apart to expand the spinal implant 20 along thetransverse axis T. In still another embodiment of the invention, atleast a portion of the spinal implant 20 may be formed of a shape-memorymaterial such as, for example, Nitinol, to provide the spinal implant 20with self-expanding capabilities so as to eliminate the requirement fora separate expansion member or expansion instrument.

In the illustrated embodiment of the spinal implant 20, the branchportions 24, 26 define oppositely-disposed upper and lower bone engagingsurfaces 40, 42 having a generally flat or planar configuration, andoppositely-disposed side surfaces 44, 46 extending between the boneengaging surfaces 40, 42 and also having a generally flat or planarconfiguration. In the illustrated embodiment, the branch portions 24, 26cooperate with one another to define a substantially rectangular outercross section. However, it should be understood that other shapes andconfigurations of the spinal implant 20 and the branch portions 24, 26are also contemplated as falling within the scope of the presentinvention, including, for example, a curved or arcuate configuration, acylindrical configuration, an elliptical configuration, a conicalconfiguration, or any other suitable shape or configuration that wouldoccur to one of skill in the art.

In a further embodiment of the invention, the spinal implant 20 may beconfigured to have a cage-like configuration, with the branch portions24, 26 cooperating with one another to define a hollow interior orpassage 50 extending generally along the longitudinal axis L. However,it should be understood that other embodiments of spinal implants arealso contemplated that do not define a hollow interior, but insteaddefine a substantially solid configuration. A bone growth promotingmaterial such as, for example, a bone morphogenetic protein (BMP) orother types of bone growth promoting materials may be positioned withinthe hollow interior 50 of the spinal implant 20 to facilitate fusionwith the adjacent vertebrae. An opening or passage 52 may also bedefined through the fixed base portion 28 to provide access to thehollow interior 50 for loading the bone growth promoting material intothe hollow interior 50 and/or for receiving an end portion of aninstrument or tool therethrough for engagement with the expansion member30 to transition the spinal implant 20 to the expanded configuration.

Although not specifically illustrated in the drawing figures, in otherembodiments of the invention, each of the branch portions 24, 26 maydefine at least one bone in-growth opening or window (not shown)extending through the bone engaging surfaces 40, 42 and/or the sidesurfaces 44, 46 and communicating with the hollow interior 50. As shouldbe appreciated, the bone in-growth openings or windows permit bonegrowth from the adjacent vertebrae and into and possibly through thespinal implant 20. In further embodiments of the invention, the boneengaging surfaces 40, 42 may define a number of bone anchoring elements(not shown) adapted for engagement with the adjacent vertebrae toprevent or inhibit movement of the spinal implant 20 once implantedwithin the intervertebral disc space. In a specific embodiment, the boneanchoring elements may comprise surface irregularities extending along asubstantial portion of the length of the spinal implant 20. For example,various types and configurations of surface projections may be providedincluding, for example, ridges, teeth, spikes, threads, surfaceroughening, or any other suitable bone anchoring element that wouldoccur to one of skill in the art.

In order to facilitate expansion of the spinal implant 20 along thetransverse axis T, the branches 24, 26 are separated from one another bya wire-like slot or channel 60 extending longitudinally from the distalend 22 b toward the proximal end 22 a and terminating adjacent the fixedbase portion 28. The slot 60 extends laterally through the spinalimplant 20 so as to divide the spinal implant 20 into two discrete upperand lower branch portions 24, 26. In embodiments where the spinalimplant 20 defines a hollow interior 50, the spinal implant 20 defines apair of oppositely disposed slots 60 extending from respective sidesurfaces 44, 46 and into communication with the hollow interior 50.However, in embodiments where the spinal implant 20 defines asubstantially solid configuration, the spinal implant 20 may define asingle slot extending laterally therethrough between the side surfaces44, 46.

In one embodiment, the slots 60 terminate at an enlarged slot portion 66adjacent the fixed base portion 28 to increase flexibility at theinterconnection location between the branch portions 24, 26 and thefixed base portion 28 so as to facilitate transitioning of the spinalimplant 20 to an expanded configuration, while at the same time tendingto decrease stress concentrations which might otherwise develop at theinterconnection location. The enlarged slot portion 66 may also be usedas a means for receiving a corresponding portion of an instrument ortool to aid in the manipulation and handing of the spinal implant 20.

In the illustrated embodiment of the spinal implant 20, the slots 60have an undulating or wavy configuration extending generally along thelongitudinal axis L such that the branch portions 24, 26 define a numberof projections or peaks that are disposed within a corresponding numberof recesses or valleys, with the projections and recesses each extendinggenerally along the transverse axis T. As illustrated in FIG. 1, theshape and configuration of the slots 60 provide the upper branch portion24 with a number of projections or peaks 62 a that are nested within acorresponding number of recesses or valleys 64 a defined by the lowerbranch portion 26. Similarly, the lower branch portion 24 is providedwith a number of projections or peaks 62 b that are nested within acorresponding number of recesses or valleys 64 b defined by the upperbranch portion 24. As a result, the projections 62 a, 62 b are nestedwithin the recesses 64 a, 64 b in an interdigitating or puzzle-likemanner, the purpose of which will be discussed below.

In one specific embodiment, the width w of the slots 60 is narrow so asto provide a relatively close or congruent fit between theaxially-facing surfaces 66 of the projections 62 a, 62 b and theaxially-facing surfaces 68 of the corresponding recesses 64 a, 64 b. Ina further embodiment, the axially-facing surfaces 66, 68 each extendgenerally along a radial arc relative to the pivot axis P. In thismanner, adjacent axially-facing surfaces 66, 68 and adjacent projections62 a, 62 b will not interfere with one another as the upper and lowerbranches 24, 26 are separated or splayed apart during expansion of thespinal implant 20. Although a specific configuration of the slots 60 hasbeen illustrated and described herein, it should be understood thatother suitable slot configurations are also contemplated as fallingwithin the scope of the present invention.

Referring to FIG. 4, illustrated therein is the spinal implant 20 showin an expanded configuration. As discussed above, the upper and lowerbranch portions 24, 26 are pivotally displaced away from one anotherrelative to the pivot axis P to transition the spinal implant 20 fromthe initial, non-expanded configuration illustrated in FIG. 1 to theexpanded configuration illustrated in FIG. 4. Additionally, duringexpansion of the spinal implant 20, the projections 62 a, 62 b areradially displaced along the recesses 64 a, 64 b relative to the pivotaxis P. When transitioned to the expanded configuration, the boneengaging surfaces 40, 42 are angled relative to one another so as toprovide the spinal implant 20 with a configuration corresponding to theparticular geometry associated with the intervertebral disc space (e.g.,the lordotic angle between the adjacent vertebrae). In one embodiment,the bone engaging surfaces 40, 42 define a taper angle A falling withina range of 0 degrees to about 30 degrees. In a more specific embodiment,the taper angle A is approximately 10 degrees. However, it should beunderstood that other taper angles A are also contemplated as fallingwithin the scope of the present invention.

As the spinal implant 20 is transitioned to the expanded configuration,portions of the projections 62 a, 62 b are maintained within thecorresponding recesses 64 a, 64 b in an interdigitating or interlockingmanner to provide structural support to the expanded spinal implant 20.As should be appreciated, engagement between the axially-facing surfaces66 of the projections 62 a, 62 b and the axially-facing surfaces 68 ofthe recesses 64 a, 64 b resists physiologic loading of the spinalimplant 20 in the direction of the longitudinal axis L, and moreparticularly shear loading forces F_(s) exerted onto the spinal implantby the adjacent vertebrae. Additionally, engagement of the projections62 a, 62 b within the recesses 64 a, 64 b resists buckling of therelatively thin fixed base portion 28 in response to the compressiveloading forces F_(c) exerted onto the spinal implant by the adjacentvertebrae. As should be appreciated, the close congruity andinterdigitating fit of the projections 62 a, 62 b within the recesses 64a, 64 b provide structural support to the spinal implant 20 whichresists physiologic shearing and bucking loading without significantlyimpeding or effecting the expansion characteristics of the spinalimplant 20.

Referring to FIGS. 5 and 6, illustrated therein is an expandable spinalimplant 120 according to another form of the present invention. Thespinal implant 120 extends along a longitudinal axis L and isstructurally similar to the spinal implant 20 illustrated and describedabove, including upper and lower branch portions 124, 126 interconnectedby a fixed base portion 128, and with the branch portions 124, 126defining upper and lower bone engaging surfaces 140, 142. However,unlike the bone engaging surfaces 40, 42 of the spinal implant 20 whichare initially arranged generally parallel to one another when in theinitial non-expanded configuration (FIG. 1), the bone engaging surfaces140, 142 of the spinal implant 120 are angled relative to one anotherwhen in an initial non-expanded configuration (FIG. 5).

As illustrated in FIG. 5, when in the initial non-expandedconfiguration, the bone engaging surfaces 140, 142 of the branchportions 124, 126 are angled relative to the longitudinal axis L toprovide the spinal implant 120 with a tapered configuration tofacilitate insertion of the spinal implant 120 into the intervertebraldisc space and/or to facilitate distraction of the adjacent vertebrae.In one embodiment, each of the bone engaging surfaces 140, 142 aretapered at an angle θ relative to the longitudinal axis L so as toprovide the spinal implant 120 with an initial overall taper angle α. Inone specific embodiment, the angle θ falls within a range of 0 degreesto about 15 degrees to provide the spinal implant 120 with an initialoverall taper angle α of between 0 degrees to about 30 degrees. In amore specific embodiment, the angle θ is approximately 5 degrees toprovide the spinal implant 120 with an initial overall taper angle α ofapproximately 10 degrees. However, it should be understood that otherangles θ and initial overall taper angles α are also contemplated asfalling within the scope of the present invention.

As illustrated in FIG. 6, when transitioned to the expandedconfiguration, the bone engaging surfaces 140, 142 of the branchportions 124, 126 are angled relative to one another so as to providethe spinal implant 120 with a configuration corresponding to theparticular geometry associated with the intervertebral disc space (e.g.,the lordotic angle between the adjacent vertebrae). Additionally,expansion of the spinal implant 120 may also serve to distract theintervertebral disc space in addition to restoring and/or maintaininglordosis between the adjacent vertebrae. In one embodiment, the boneengaging surfaces 140, 142 are tapered relative to one another so as toprovide the spinal implant 120 with an expanded taper angle A. In aspecific embodiment, the expanded taper angle A falls within a range ofbetween 0 degrees to about 30 degrees. In another specific embodiment,the expanded taper angle A is approximately 10 degrees. However, itshould be understood that other expanded taper angles A are alsocontemplated as falling within the scope of the present invention.

Referring to FIG. 7, illustrated therein is an expandable spinal implant220 according to another form of the present invention. The spinalimplant 220 extends along a longitudinal axis L and is structurallysimilar to the spinal implant 20 illustrated and described above,including a proximal end portion 222 a, a distal end portion 222 b, andupper and lower branch portions 224, 226 interconnected by a fixed baseportion 228 in a manner which allows the branch portions 224, 226 tomove relative to one another to expand the spinal implant 220 generallyalong a transverse axis T. In the illustrated embodiment, expansion ofthe spinal implant 220 results from relative pivotal movement of thebranch portions 224, 226 about a pivot axis P positioned along the fixedbase portion 228. However, other types of relative movement between thebranch portions 224, 226 are also contemplated as falling within thescope of the present invention. In one embodiment, expansion of thespinal implant 220 occurs in response to axial displacement of anexpansion member 230 (shown in phantom) along a pair of opposing taperedsurfaces 232, 234 defined by the branch portions 224, 226, which in turnwedges the branch portions 224, 226 apart to expand the spinal implant220 along the transverse axis T. Additionally, the tapered surfaces 232,234 define a retention element or recess 236 configured to retain orlock the expansion member in a select axial position relative to thespinal implant 220 and to maintain the spinal implant 220 in a selectexpanded configuration.

In order to facilitate expansion of the spinal implant 220 along thetransverse axis T, the branches 224, 226 are separated from one anotherby a wire-like slot or channel 260 extending longitudinally from thedistal end 222 b of the spinal implant 220 toward the proximal end 222 aand terminating adjacent the fixed base portion 228. The slot 260extends laterally through the spinal implant 220 so as to divide thespinal implant 220 into two discrete upper and lower branch portions224, 226. In the illustrated embodiment, the slot 260 terminates at anenlarged slot portion 266 adjacent the fixed base portion 228 toincrease flexibility at the interconnection location between the branchportions 224, 226 and the fixed base portion 228 to facilitatetransitioning of the spinal implant 220 to an expanded configuration,while at the same time tending to decrease stress concentrations whichmight otherwise develop at the interconnection location. In oneembodiment, the slot 260 includes a U-shaped portion that provides thebranch portions 224, 226 with a projection 262 nested within acorresponding recess 264, with the projection 262 and recess 264extending generally along the transverse axis T. In the illustratedembodiment, the shape and configuration of the slot 260 provides theupper branch portion 224 with the recess 264 and the lower branchportion 226 with the projection 262, however, a reverse configuration isalso contemplated. The projection 262 is nested within the recess 264 inan interdigitating or puzzle-like manner.

In one embodiment, the width w of the slot 260 is narrow so as toprovide a relatively close or congruent fit between the axially-facingsurfaces 266 of the projection 262 and the axially-facing surfaces 268of the recess 264. In a further embodiment, the axially-facing surfaces266, 268 each extend generally along a radial arc relative to the pivotaxis P. In this manner, the opposing axially-facing surfaces 266, 268will not interfere with one another as the upper and lower branches 224,226 are separated or splayed apart during expansion of the spinalimplant 220. Although a specific configuration of the slots 260 has beenillustrated and described herein, it should be understood that othersuitable slot configurations are also contemplated as falling within thescope of the present invention.

As should be appreciated, during expansion of the spinal implant 220,the projection 262 is radially displaced along the recess 264 relativeto the pivot axis P. As the spinal implant 220 is transitioned to theexpanded configuration, a portion of the projection 262 is maintainedwithin the recess 264 in an interdigitating or interlocking manner toprovide structural support to the expanded spinal implant 220.Engagement between the axially-facing surfaces 266 of the projection 262and the axially-facing surfaces 268 of the recess 264 resistsphysiologic loading of the spinal implant 220 in the direction of thelongitudinal axis L, and more particularly shear loading forces exertedonto the spinal implant by the adjacent vertebrae. Additionally,engagement of the projection 262 within the recess 264 resists bucklingof the relatively thin fixed base portion 228 in response to thecompressive loading forces exerted onto the spinal implant by theadjacent vertebrae. Moreover, the close congruity and interdigitatingfit of the projection 262 within the recess 264 provide structuralsupport to the spinal implant 220 which resists physiologic shear andbucking loading without significantly impeding or effecting theexpansion characteristics of the spinal implant 220.

Referring to FIG. 8, illustrated therein is an expandable spinal implant320 according to another form of the present invention. The spinalimplant 320 extends along a longitudinal axis L and is configured toexpand generally along a transverse axis T so as to distract anintervertebral disc space and/or to restore or maintain lordosis betweenthe adjacent vertebrae. However, it should be understood that expansionof the spinal implant 320 may occur in multiple directions and alongmultiple axes. In the illustrated embodiment, expansion of the spinalimplant 320 results from relative pivotal movement of the branchportions 324, 326 about a pivot axis P positioned along the fixed baseportion 328. However, other types of relative movement between thebranch portions 324, 326 are also contemplated as falling within thescope of the present invention.

In one embodiment, expansion of the spinal implant 320 occurs inresponse to axial displacement of an expansion member (not shown)generally along the longitudinal axis L, which in turn separates thebranch portions 324, 326 apart to expand the spinal implant 320 alongthe transverse axis T. Additionally, the spinal implant 320 includes aretention element or step feature 336 configured for engagement by theexpansion member to secure the spinal implant in a select expandedconfiguration. In the illustrated embodiment, the retention element 336comprises a pair of adjacent openings 338 a, 338 b extending through theupper and lower branch portions 324, 326 which are sized and shaped toreceive corresponding portions of the expansion member therein. Theexpansion member is engaged and retained within each of the openings 338a, 338 b and separates the upper and lower branch portions 324, 326apart in an incremental manner so as to incrementally expand the spinalimplant 320 along the transverse axis T.

In the illustrated embodiment, the branch portions 324, 326 defineoppositely-disposed upper and lower bone engaging surfaces 340, 342 eachhaving a generally flat or planar configuration, and oppositely-disposedside surfaces 344, 346 extending between the bone engaging surfaces 340,342 and also having a generally flat or planar configuration. In oneembodiment, the branch portions 324, 326 cooperate with one another todefine a substantially rectangular outer cross section. However, itshould be understood that other shapes and configurations of the spinalimplant 320 and the branch portions 324, 326 are also contemplated asfalling within the scope of the present invention.

In a further embodiment of the invention, the branch portions 324, 326cooperate with one another to define a hollow interior or passage 350extending generally along the longitudinal axis L. However, it should beunderstood that other embodiments of spinal implants are alsocontemplated that do not define a hollow interior, but instead define asubstantially solid configuration. A bone growth promoting material maybe positioned within the hollow interior 350 of the spinal implant 320to facilitate fusion with the adjacent vertebrae. Additionally, anopening or passage 352 is defined through the fixed base portion 328 toprovide access to the hollow interior 350 for loading the bone growthpromoting material into the hollow interior 350 and/or for receiving anend portion of an instrument or tool therethrough and into engagementwith the expansion member to transition the spinal implant 320 to theexpanded configuration. The spinal implant 320 may also define an opendistal end 353. Additionally, each of the branch portions 324, 326defines at least one bone in-growth opening or window 354 extendingthrough the bone engaging surfaces 340, 342 and communicating with thehollow interior 350 to permit bone growth from the adjacent vertebraeand into and possibly through the spinal implant 320.

In a further embodiment of the invention, the bone engaging surfaces340, 342 may define a number of bone anchoring elements adapted forengagement with the adjacent vertebrae to prevent or inhibit movement ofthe spinal implant 320 once implanted within the intervertebral discspace. In the illustrated embodiment, the bone anchoring elementsinclude a series of grooves 356 and a series of teeth 358. However, itshould be understood that other types of bone anchoring elements arealso contemplated including, for example, ridges, spikes, threads,surface roughening, or other suitable types and configurations of boneanchoring elements.

In order to facilitate expansion of the spinal implant 320 along thetransverse axis T, the branches 324, 326 are separated from one anotherby a wire-like slot or channel 360 extending longitudinally from thedistal end 322 b toward the proximal end 322 a and terminating adjacentthe fixed base portion 328. The slot 360 extends laterally through thespinal implant 320 so as to divide the spinal implant 320 into twodiscrete upper and lower branch portions 324, 326. In the illustratedembodiment, the slot 360 terminate at an enlarged slot portion 366adjacent the fixed base portion 328 to increase flexibility at theinterconnection location between the branch portions 324, 326 and thefixed base portion 328 to facilitate transitioning of the spinal implant320 to an expanded configuration, while at the same time tending todecrease stress concentrations which might otherwise develop at theinterconnection location. Additionally, the enlarged slot portion 366also provides additional passageways for bone in-growth into the hollowinterior 350. The enlarged slot portion 366 may also be used as a meansfor receiving a corresponding portion of an instrument or tool to aid inthe manipulation and handing of the spinal implant 320.

In the illustrated embodiment, the slot 360 includes a U-shaped portionthat provides the branch portions 324, 326 with a projection 362 nestedwithin a corresponding recess 364, with the projection 362 and therecess 364 extending generally along the transverse axis T. In oneembodiment, the shape and configuration of the slot 360 provides theupper branch portion 324 with the recess 364 and the lower branchportion 326 with the projection 362, however, a reverse configuration isalso contemplated. The projection 362 is nested within the recess 364 ina puzzle-like manner.

In one embodiment of the invention, the width w of the slots 360 isnarrow to provide a relatively close or congruent fit between theaxially-facing surfaces 366 of the projection 362 and the axially-facingsurfaces 368 of the recess 364. In a further embodiment, theaxially-facing surfaces 366, 368 each extend generally along a radialarc relative to the pivot axis P. In this manner, the opposingaxially-facing surfaces 366, 368 will not interfere with one another asthe upper and lower branches 324, 326 are separated or splayed apartduring expansion of the spinal implant 320. Although a specificconfiguration of the slots 360 has been illustrated and describedherein, it should be understood that other suitable slot configurationsare also contemplated as falling within the scope of the presentinvention.

As should be appreciated, during expansion of the spinal implant 320,the projection 362 is radially displaced along the recess 364 relativeto the pivot axis P. As the spinal implant 320 is transitioned to theexpanded configuration, a portion of the projection 362 is maintainedwithin the recess 364 in an interdigitating or interlocking manner toprovide structural support to the expanded spinal implant 320.Engagement between the axially-facing surfaces 366 of the projection 362and the axially-facing surfaces 368 of the recess 364 resistsphysiologic loading of the spinal implant 320 in the direction of thelongitudinal axis L, and more particularly shear loading forces exertedonto the spinal implant by the adjacent vertebrae. Additionally,engagement of the projection 362 within the recess 364 resists bucklingof the relatively thin fixed base portion 328 in response to thecompressive loading forces exerted onto the spinal implant by theadjacent vertebrae. Moreover, the close congruity and interdigitatingfit of the projection 362 within the recess 364 provide structuralsupport to the spinal implant 320 which resists physiologic shear andbucking loading without significantly impeding or effecting theexpansion characteristics of the spinal implant 320.

Referring to FIGS. 9 and 10, illustrated therein an expandable spinalimplant 420 according to another form of the present invention. Theillustrated embodiment of the spinal implant 420 extends along alongitudinal axis L and is in many respects structurally similar to thespinal implant 320 illustrated and described above, including upper andlower branch portions 424, 426 interconnected by a fixed base portion428 in a manner allowing expansion of the spinal implant 420 generallyalong a transverse axis T. Additionally, in order to facilitateexpansion of the spinal implant 420 along the transverse axis T, thebranches 424, 426 are separated from one another by a wire-like slot orchannel 460 extending longitudinally from the distal end 422 b of thespinal implant 420 toward the proximal end 422 a and terminatingadjacent the fixed base portion 428. The slot 460 extends laterallythrough the spinal implant 420 so as to divide the spinal implant 420into two discrete upper and lower branch portions 424, 426.

In the illustrated embodiment, the slot 460 terminates at an enlargedslot portion 466 adjacent the fixed base portion 428 to increaseflexibility at the interconnection location between the branch portions424, 426 and the fixed base portion 428 to facilitate transitioning ofthe spinal implant 420 to an expanded configuration, while at the sametime tending to decrease stress concentrations which might otherwisedevelop at the interconnection location. The slot 460 includes also aU-shaped portion that provides the branch portions 424, 426 with aprojection or post 462 nested within a corresponding recess or channel464, with the projection 462 and the recess 464 extending generallyalong the transverse axis T. In one embodiment, the shape andconfiguration of the slot 460 provides the upper branch portion 424 withthe recess 464 and the lower branch portion 426 with the projection 462,however, a reverse configuration is also contemplated.

The projection 462 is nested within the recess 464 in a puzzle-likemanner. In the illustrated embodiment, the projection 462 and the recess464 each define a number of retention elements 436 to maintain thespinal implant 420 in a select expanded configuration. In oneembodiment, the retention elements 436 comprise a number of snap membersor ratchets/pawls 438 a defined transversely along the projection 462and a number of snap members or ratchets/pawls 438 b definedtransversely along the recess 464. In a further embodiment, a pluralityof the ratchets/pawls 438 a, 438 b are defined along each of theprojection 462 and the recess 464. However, it should be understood thatin other embodiments, either the projection 462 or the recess 464 maydefine a single ratchet/pawl 438 a, 438 b.

As should be appreciated, the ratchets/pawls 438 a, 438 b serve asretention elements or interlock features that retain or lock the spinalimplant 420 in a select expanded configuration. As should also beappreciated, the ratchets/pawls 438 a, 438 b cooperate with one anotherto allow the upper and lower branch portions 424, 426 to be displacedapart during incremental expansion of the spinal implant 420, while atthe same time preventing displacement of the upper and lower branchportions 424, 426 toward one another subsequent to expansion to therebymaintain the spinal implant 420 in a select expanded configuration.Although a specific embodiment of the retention elements 436 has beenillustrated and described herein, it should be understood that othertypes and configurations of retention elements or interlock featuressuitable for maintaining the spinal implant 420 in a select expandedconfiguration are also contemplated.

Referring to FIG. 10, during expansion of the spinal implant 420, theprojection 462 is displaced along the recess 464, with a portion of theprojection 462 maintained within the recess 464 and with theratchets/pawls 438 a, 438 b engaged in an interdigitating orinterlocking manner to maintain the spinal implant 420 in a selectexpanded configuration and to provide structural support to the expandedspinal implant 420. Engagement of the projection 462 within the recess464 also resists physiologic loading of the spinal implant 420 in thedirection of the longitudinal axis L, and more particularly shearloading forces exerted onto the spinal implant by the adjacentvertebrae. Additionally, engagement of the projection 462 within therecess 464 resists buckling of the relatively thin fixed base portion428 in response to the compressive loading forces exerted onto thespinal implant by the adjacent vertebrae. Moreover, the close congruityand interdigitating fit of the projection 462 within the recess 464provides structural support to the spinal implant 420 which resistsphysiologic shear and bucking loading without significantly impeding oreffecting the expansion characteristics of the spinal implant 420.

In one embodiment, a spreader or distractor-type instrument (not shown)having first and second end portions engaged with the upper and lowerbranch portions 424, 426, respectively, may be used to exert an outwardforce onto the branch portions 424, 426 to transition the implant 420 toan expanded configuration. However, other devices and techniques may beused to expand the spinal implant 420 such as, for example, via awedge-type expansion member similar to the expansion member 30illustrated and described above with regard to the spinal implant 20.

In one embodiment of the invention, access to the spinal column andinsertion of the spinal implants into the intervertebral disc space isaccomplished via a posterior surgical approach. However, it should beunderstood that access to and insertion of the spinal implants into theintervertebral disc space may be accomplished via other surgicalapproaches, such as, for example, an anterior approach or a lateralapproach. In another embodiment of the invention, the spinal implantsare used to treat the lumbar region of the spine. However, it shouldnevertheless be understood that the present invention is also applicableto other portions of the spine, including the cervical, thoracic orsacral regions of the spine. Additionally, in a further embodiment ofthe invention, a pair of spinal implants may be positioned side-by-sidein a bilateral arrangement within the intervertebral disc space.However, it should be understood that unilateral placement or centralplacement of a single spinal implant embodiment within theintervertebral disc space is also contemplated as falling within thescope of the present invention.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

1. An expandable spinal implant, comprising: a body extending generallyalong a longitudinal axis between a first end portion and a second endportion, said body defining at least one slot extending generally alongsaid longitudinal axis from said first end portion toward said secondend portion to provide said body with at least two expandable branchportions formed together adjacent said second end portion so as todefine a single-piece unitary implant body, said body including aplurality of transverse projections defined by a first of said branchportions each comprising an arcuate surface extending between a pair ofplanar side surfaces, said body further including a plurality oftransverse recesses defined by a second of said branch portions eachcomprising an arcuate surface extending between a pair of planar sidesurfaces, said planar side surfaces of said transverse recesses engagingsaid planar side surfaces of a respective transverse projection and saidarcuate surface of said transverse recesses engaging an arcuate surfaceof a respective transverse projection to provide structural support tothe implant subsequent to expansion; and a retention element extendingtransversely between and engaged with said at least two branch portionssubsequent to expansion of the implant to maintain said body in anexpanded configuration.
 2. The implant of claim 1, wherein saidtransverse projections are positioned within and displacable along saidtransverse recesses to provide close fitting interlocking featuresbetween said branch portions that provide said structural support to theimplant subsequent to expansion.
 3. The implant of claim 1, wherein saidtransverse portions define oppositely facing outer surfaces positionedin close proximity with respective opposing inner surfaces of saidtransverse recesses to provide close fitting interlocking featuresbetween said branch portions that provide said structural support to theimplant subsequent to expansion.
 4. The implant of claim 1, wherein saidbranch portions are pivotally displaced relative to one another about apivot axis during expansion of the implant, each of said transverseprojections and a respective transverse recess defining an adjacent pairof surfaces having generally the same radius of curvature relative tosaid pivot axis.
 5. The implant of claim 1, wherein said branch portionsare coupled together adjacent said second end portion of said body toallow relative pivotal movement therebetween about a pivot axis, saidtransverse projections each extending generally along a radial arcrelative to said pivot axis, a respective transverse recess alsoextending generally along said radial arc.
 6. The implant of claim 1,wherein said branch portions are coupled together adjacent said secondend portion of said body to allow relative pivotal movement therebetweenabout said pivot axis, said transverse projections each having anarcuate outer surface extending generally along a radial arc relative tosaid pivot axis, a respective transverse recess having an arcuate innersurface extending generally along said radial arc, said arcuate outersurfaces of said transverse projections being positioned in closeproximity with said arcuate inner surfaces of said transverse recessesto provide said structural support to the implant subsequent toexpansion.
 7. The implant of claim 1, wherein said transverseprojections and said transverse recesses define a number of interlockingretention elements configured to maintain the implant in said expandedconfiguration.
 8. The implant of claim 7, wherein said interlockingretention elements comprise interlocking ratchet elements.
 9. Theimplant of claim 1, wherein said second end portion of said body has anouter surface facing away from said branch portions, said outer surfacedefining a concave curvature to facilitate expansion of the implant. 10.The implant of claim 1, wherein said slot includes an enlarged portionadjacent said second end of said body to facilitate expansion of theimplant.
 11. The implant of claim 1, wherein said slot has an undulatingcurved configuration.
 12. The implant of claim 1, wherein said branchportions include a pair of opposing notches sized and shaped tointerlockingly engage and retain said retention element in a selectposition upon expansion of the implant.
 13. The implant of claim 1,wherein said at least two expandable branch portions cooperate to definea hollow interior of said body; and further comprising a bone growthpromoting substance disposed within said hollow interior to facilitatefusion with adjacent vertebrae.
 14. An expandable spinal implant,comprising: at least two expandable branch portions extending generallyalong a longitudinal axis, each of said branch portions including afixed end portion and an opposite movable end portion with each of saidfixed end portions formed together adjacent a fixed base portion of theimplant, a first of said branch portions defining a plurality oftransverse projection projections each comprising an arcuate surfaceextending between a pair of planar side surfaces and a second of saidbranch portions defining a plurality of transverse recesses eachcomprising an arcuate surface extending between a pair of planar sidesurfaces, said planar side surfaces of said transverse projectionsengaging said planar side surfaces of a respective transverse recess andsaid arcuate surface of said transverse projections engaging saidarcuate surface of a respective transverse recess to provide structuralsupport to the implant subsequent to expansion, said first and secondbranch portions being formed together so as to define a single-pieceunitary implant body; and a retention element extending transverselybetween and engaged with said at least two branch portions subsequent toexpansion of the implant to maintain said body in an expandedconfiguration.
 15. The implant of claim 14, wherein said transverseprojections are positioned within and displacable along said transverserecesses to provide close fitting interlocking features between saidbranch portions that provide said structural support to the implantsubsequent to expansion.
 16. The implant of claim 14, wherein saidtransverse projections define oppositely facing outer surfacespositioned in close proximity with respective inner surfaces of saidtransverse recesses to provide close fitting interlocking featuresbetween said branch portions that provide said structural support to theimplant subsequent to expansion.
 17. The implant of claim 14, whereinsaid branch portions are coupled together adjacent said second endportion of said body to allow relative pivotal movement therebetweenabout said pivot axis, said transverse projections each having anarcuate outer surface extending generally along a radial arc relative tosaid pivot axis, a respective transverse recess having an arcuate innersurface extending generally along said radial arc, said arcuate outersurfaces of said transverse projections being positioned in closeproximity with said arcuate inner surfaces of said transverse recessesto provide said structural support to the implant subsequent toexpansion.
 18. The implant of claim14, wherein said branch portions areformed integral with said second end portion of said body to define asingle-piece unitary implant body.
 19. The implant of claim 14, whereinsaid branch portions include a pair of opposing notches sized and shapedto interlockingly engage and retain said retention element in a selectposition upon expansion of the implant.